1. Field of the Invention
This invention relates to the encoding of audio signals and, more particularly, to improved transform coding of digitized audio signals.
2. Background Description
The need for low bitrate and low delay audio coding, such as is required for video conferencing over modern digital data communications networks, has required the development of new and more efficient schemes for audio signal coding.
Transform coding is one of the best known techniques for high quality audio signal coding in low bitrates, because of extensive use of psychoacoustic models for noise masking. A general description of transform coding techniques can be found in "Transform Coding of Audio Signals Using Perceptual Noise Criteria", IEEE Journal of Selected Areas in Comm., February 1988, J. D. Johnston.
In the low delay case, however, transform coding is difficult to apply since the need to use a short transform results in low coding gain.